Just keep rolling a lawn ION's autonomous mowers: you might not know it from your own backyard performance, but mowing a lawn accurately and precisely constitutes a difficult systems problem, requiring centimeter-level accuracy and precision control for straight lines and smooth turns. Three student teams answered the Institute of Navigation's call to produce a smarter-than-the-average lawnmower

GPS World, Sept, 2004 by Mikel Miller, John Raquet, Jade Morton, Frank Van Graas, Boris Pervan, Laura O'Rear

Servo System. Two servo motors and controllers are used on the lawn mower. The servos are attached to the control shaft of the hydrostatic pump on each wheel. The position of the control shaft determines how fast each wheel moves and in which direction (forward or reverse). The servos are linked to the control shaft through a gear system, where they convert voltage inputs into physical movement. Controlling the position of each servo controls and/or predicts the speed and location of the mower.

Base Mower. A 42-inch hydrostatic lawnmower served as the base unit for the Red Blade. The major reason to choose the hydrostatic mower was the capability of controlling each drive wheel independently. Many other mechanical features added to the mower make it self-sufficient and user-friendly. These modifications provide Red Blade with the proper structure, support, and protection for all of its components. Other modifications added safety and ease of use when operating. Specific modifications include the servo support system, the protective Pelican electronics case and stand, the dash board, a kick stand, the GPS and compass stand, the magnet sensing system, and the wiring.

Control Panel. A custom dashboard contained the appropriate user operating devices such as the throttle, ignition, and blade control, previously located on the handlebars. Initially, the handlebars did not meet ION specifications for mower height. They also inhibited autonomous control and were therefore removed. An emergency stop switch, hardwired into the kill switch of the ignition, was placed on top of the dashboard. A remote control E-stop was also mounted on the back side of the dash.

The GPS and compass stand (made of PVC, unistrut beams, and t-joints) provide the compass and GPS receiver with a safe and sturdy location for operation. The GPS receiver/antenna was raised above the stand to help eliminate potential multipath errors as well as provide the antenna with an unob-structed view of the sky. Further, the compass was positioned directly over the central axis of the lawnmower to provide accurate orientation readings.

Team Members. Brett McNally (team leader), Micah Stutzman, Collin Koranda, Chris Mantz, Jeff Macasek, Scott Miller, Andrew Walker (undergraduates); Jade Morton, Scott Campbell, and James Leonard (faculty advisors).

Illinois Institute of Technology

The IIT lawnmower prototype consists of two units: the vehicle ("Leonard"), containing the navigation sensors, computer, and power supply, and providing motion and steering; and the grass-cutting device, a standard off-the-shelf electric lawnmower.

The mobile platform was not specifically built for mowing missions, but was designed with flexibility to accommodate various tools and sensors. This modular structure provides the advantage of use not only for lawnmowing, but also spreading fertilizer and seeds, sweeping concrete surfaces, or removing snow. From a marketing perspective, this versatility becomes a decisive asset (Figure 3).